Utilizing the Multiradionuclide Resolving Power of SPECT and Dual Radiolabeled Single Molecules to Assess Treatment Response of Tumors

作者：Xu Baogang; Shokeen Monica; Sudlow Gail P; Harpstrite Scott E; Liang Kexian; Cheney Philip P; Edwards W Barry; Sharma Vijay; Laforest Richard; Akers Walter J; Achilefu Samuel^*

来源：Molecular Imaging and Biology, 2015, 17(5): 671-679.

DOI：10.1007/s11307-015-0842-8

• Cancer
• Apoptosis
• Caspase
• Programmed cell death
• Radionuclide
• SPECT
• Cleavable peptide

Single photon emission computed tomography (SPECT) radionuclide pairs having distinct decay rates and different energy maxima enable simultaneous detection of dual gamma signals and real-time assessment of dynamic functional and molecular processes in vivo. Here, we report image acquisition and quantification protocols for a single molecule labeled with two different radionuclides for functional SPECT imaging.
LS370 and LS734 were prepared using modular solid phase peptide synthesis. Each agent has a caspase-3 cleavable reporting motif, flanked by a tyrosine residue and a chelator at the opposite end of molecule. Cell uptake and efflux were assessed in human MDA-MB-231 breast cancer cells. Biodistribution studies were conducted in tumor naive and orthotopic 4T1 metastatic breast cancer tumor mice. NanoSPECT dual-imaging validation and attenuation correction parameters were developed using phantom vials containing varying radionuclide concentrations. Proof-of-principle SPECT imaging was performed in MMTV-PyMT transgenic mice.
LS370 and LS734 were singly or dually radiolabeled with I-125 and In-111 or Tc-99m. Cell assays demonstrated 11-fold higher percent uptake (P < 0.001) of [I-125]LS734 (3.6 +/- 0.5) compared to [I-125]LS370 (0.3 +/- 0.3) at 2 h. Following chemotherapy, cellular retention of [I-125]LS734 was 3-fold higher (P < 0.05) than untreated cells. Pharmacokinetics at 1 h postinjection demonstrated longer blood retention (%ID/g) for [I-125]LS734 (3.2 +/- 0.9) compared to [I-125]LS370 (1.6 +/- 0.1). In mice bearing bilateral orthotopic 4T1 tumors, the uptake (%ID/g) was 2.4 +/- 0.3 for [I-125]LS734 and 1.2 +/- 0.03 for [I-125]LS370. The iodinated tyrosine peptide residue label was stable under in vitro conditions for up to 24 h; rapid systemic deiodination (high thyroid uptake) was observed in vivo. Phantom studies using standards demonstrated deconvolution of radionuclide signals based on different gamma ray energies. In MMTV-PyMT mice imaged with dual-labeled [In-111]-[I-125]LS734, the gamma signals were separable and quantifiable.
Image processing protocols were developed for quantitative signal separation resulting from a caspase-3 responsive dual-radiolabeled SPECT probe. Crosstalk unmixing was obtained for multiradionuclide NanoSPECT imaging. In vitro and in vivo data demonstrated structure-activity relationships for developing functional agents for ratiometric SPECT imaging.

• 出版日期2015-10